1. Field of Invention
The invention relates to a white balance method and, in particular, to a white balance process for color digital images.
2. Related Art
Nowadays, there are more and better digital products and coding technologies introduced to the world. The demand of a digital life has become the new driving force for the digital technology to develop toward a wider space. Digital products such as computers, cell phones, video cameras, digital cameras, PDA's are changing our daily life. It is believed that more new digital products will be developed and affect our life in the future. The developments in basic structures and functioning principles of the digital image technology are also subjects that scientists are after.
White balance is a basic function in color digital image equipment. This function defines “white” as “white” no matter how the environmental light changes. When the colors on a real object are recorded using a color sensor, there might be deviations existing between the recorded colors and the actual colors. Only when an appropriate light source with a specific color spectrum exists can the actual colors on the real object be captured. For many sensors, the sunlight is the most appropriate illuminant. When the sunlight shines on a white object, the image captured by the sensor will manifest the actual white color. However, when the same object is in the light produced by artificial white light, the image captured by the sensor tends to be slightly red. This is because the spectrum of the artificial white light has a strong red light component. When using a digital camera without the white balance function, one will discover that the white object under the artificial white light, the image is actually bluish. The image shown in FIG. 1a is obviously bluish. The reason human eyes detect the color as white is because they correct the color. The image after the white balance process will produce a satisfactory effect like FIG. 1b. The conventional AWB algorithm is used in the process by obtaining simulation results by processing a huge amount of test color images. All areas in an image have to be white balance processed. Therefore, it takes a longer processing time. It is based upon the assumption that the composite color of the whole image is white. However, this method cannot process correctly for big monochromic object or background.